The documents don't identify Exxon Mobil, but maps show a large parcel of land near Interstate 45 and the Hardy Toll Road. The company owns land near that intersection.

Exxon Mobil spokesman Alan Jeffers said as part of the study the company is considering the potential use of its land, although no decision on future office requirements will be made until after the study is completed.

The study, which looks at maintaining Exxon Mobil's current offices as well as consolidation alternatives, is expected to continue into 2011.

A principal of PDR — the Houston-based architecture firm whose name is on the documents — said her firm does work for Exxon Mobil all over the world but declined to comment further.

“We don't comment on the work we do for any of our clients,” said Joanne Taylor.

Jeffers said he wasn't in a position to comment on the veracity of the PDR documents, some of which are dated May 2009.

He also would not discuss what the study means for employees at Exxon Mobil's corporate headquarters in Irving or those working in the company's Fairfax, Va., offices. The company has maintained a presence there since it acquired Mobil Corp. a decade ago.

A move by the biggest U.S. oil and natural gas company could amount to big changes for Houston's office market.

Exxon Mobil has offices throughout the Houston area, with large concentrations of workers in the Greenspoint area and downtown.

Jack Drake, president of the Greenspoint District, said while his area could potentially lose a large tenant, its best office space is virtually full, “so a departure of a major tenant allows for the opportunity for expansion and for new companies.”

If an Exxon Mobil campus were to be built, it would provide a big boost to the north Houston community, said Trey Halberdier of BanDier Realty Partners.

“It would have a positive and significant impact on all real estate types — retail, office, residential and even industrial,” said Halberdier, whose firm sells commercial properties in the area.

Houston must OK district

While it could be some time before Exxon Mobil reveals its plans, a 1,400-acre tract west of I-45 and the Hardy Toll Road is being prepped for development. An improvement district approved by the Texas Legislature has been created to build and finance utilities and roads to serve the property west of I-45.

The Harris County Improvement District No. 18 must now be approved by the city, a process that should be completed in the next couple of months, said Andy Icken, deputy director of Public Works for the city of Houston.

One of the PDR documents shows plans for additional development south of the likely Exxon Mobil site and north of the proposed Grand Parkway.

They include a town center, medical facility, commercial space, apartments and single-family homes.

“The things we're hoping for down the road is an increase in home sales in all price ranges, more excitement in the retail sector and commercial leasing. It impacts every phase of our business,” she said.